The present invention generally relates to color video signal recording and reproducing apparatuses, and more particularly to a color video signal recording and reproducing apparatus in which a luminance signal and two kinds of color difference signals of a color video signal are respectively subjected to a time base compression by use of a digital memory and thereafter time-division-multiplexed, a frequency modulated signal which is obtained by frequency-modulating the time division multiplexed signal is recorded on a recording medium, and a frequency modulated signal which is reproduced from the recording medium is frequency-demodulated and then subjected to a time base expansion to the original time base by use of the digital memory to obtain a reproduced color video signal.
Among the existing color video signal recording and reproducing apparatuses such as video tape recorders (VTRs), the more popular recording and reproducing apparatuses separate a luminance signal and a carrier chrominance signal from a standard system composite color video signal. The standard system is a system such as the NTSC system, the PAL system, and the SECAM system. The separated luminance signal is frequency-modulated, and the separated carrier chrominance signal is frequency-converted into a low frequency range. The frequency converted carrier chrominance signal is frequency-division-multiplexed with the frequency modulated luminance signal and recorded on a recording medium. At the time of the reproduction, a signal processing opposite to the signal processing carried out at the time of the recording, is carried out to obtain a reproduced composite color video signal which is in conformance with the original standard system. In other words, the more popular recording and reproducing apparatuses employ the so-called low-band-conversion recording and reproducing system.
Other various recording and reproducing systems have been proposed besides the low-band-conversion recording and reproducing system. For example, there was a proposed recording and reproducing apparatus which was designed to subject two kinds of color difference signals which are obtained by frequency-demodulating the carrier chrominance signal to a time base compression, and also subject the luminance signal to a time base compression. According to this proposed recording and reproducing apparatus, the time base compressed signals are time-division-multiplexed, and the time division multiplexed signal is frequency-modulated and recorded on the recording medium. At the time of the reproduction, a signal processing opposite to the signal processing carried out at the time of the recording, is carried out to obtain a reproduced composite color video signal which is in conformance with the original standard system. An example of such a recording and reproducing apparatus may be found in the U.S. Pat. Nos. 3,781,463 and 4,245,235, for example. This proposed recording and reproducing apparatus takes into account the difference in the bands of the luminance signal and the color difference signals, and takes measures so that the color difference signals having the narrower band can be transmitted within the horizontal blanking period. In other words, one of the color difference signals which is transmitted within one horizontal scanning period (1 H), is subjected to a time base compression into approximately 20% of 1 H. In addition, to utilize the band effectively, the luminance signal is subjected to a time base compression into approximately 80% of 1 H so as to occupy a band which is in the same range as the band of the time base compressed color difference signal, and transmitted. Further, the two color difference signals are time-division-multiplexed, as a line-sequential signal in which the two color difference signals are alternately transmitted for every 1 H, with the time base compressed luminance signal. This time-division-multiplexed signal is supplied to a frequency modulator, and an output signal of the frequency modulator is recorded on the recording medium. At the time of the reproduction, a signal processing opposite to the signal processing carried out at the time of the recording, is carried out to obtain a reproduced composite color video signal. The recording and reproducing system employed in this proposed recording and reproducing apparatus, will hereinafter be referred to as a timeplex system.
According to the timeplex system which transmits the time-division-multiplexed signal, there is no duration in which the luminance signal and the color difference signal are transmitted simultaneously. In the case of the NTSC system color video signal and the
system color video signal, a mutual interference and moire may occur between the luminance signal and the color difference signals, because the luminance signal and the carrier chrominance signal are band-share-multiplexed and transmitted. However, such a mutual interference and moire will not occur according to the timeplex system. In addition, even when the color video signal of any one of the NTSC system, the PAL system, and the SECAM system is recorded by an azimuth recording and reproducing system on tracks having the horizontal synchronizing signals recorded in non-alignment between mutually adjacent tracks and then reproduced, there is substantially no crosstalk from the adjacent tracks due to the azimuth loss effect, and it is possible to obtain a reproduced picture of a high picture quality. This is because the time-division-multiplexed signal is recorded on the adjacent tracks in the form of a frequency modulated signal which is obtained by frequency-modulating by the time-division-multiplexed signal a high-frequency carrier which has a large azimuth loss effect.
The time base compressed luminance signal and the time base compressed color difference signal employed in the timeplex system, both have an energy distribution in which the energy is large in the low frequency range and the energy is small in the high frequency range. In other words, the time base compressed luminance signal and the time base compressed color difference signal assume a signal format which is suited for the frequency modulation. Thus, it is possible to obtain a large modulation index, and the signal-to-noise ratio can be greatly improved. Moreover, it is possible to substantially eliminate a deviation in the reproducing time base when expanding the time base.
The conventional recording and reproducing apparatus employing the timeplex system, used an analog memory such as a charge transfer element for carrying out the time base compression and the time base expansion. Consequently, each starting point of the time base compression or the time base expansion of the input signal could not be clearly determined, and it was impossible to compensate for the deviation in the reproducing time base (jitter) in a satisfactory manner. In addition, there was a problem in that the picture quality of the reproduced picture became deteriorated because the analog memory itself has a frequency characteristic in which a flat characteristic portion is relatively narrow.
Especially when recording and reproducing the SECAM system color video signal according to the timeplex system, the carrier chrominance signal in the SECAM system color video signal is a line-sequential signal in which a first frequency modulated signal obtained by frequency-modulating a first carrier by a color difference signal (R-Y) and a second frequency modulated signal obtained by frequency-modulating a second carrier by a color difference signal (B-Y) are alternately time-sequentially multiplexed for every 1 H, as is well known, and the color difference signals (R-Y) and (B-Y) which are obtained by frequency-demodulating the above carrier chrominance signal are naturally in the form of a line-sequential color difference signal. For this reason, when recording the SECAM system color video signal by the conventional recording and reproducing apparatus, the frequency demcdulated line-sequential color difference signal was passed through a circuit which simultaneously obtained the color difference signals (R-Y) and (B-Y), and then the color difference signals were supplied to a switching circuit part which produced the above line-sequential color difference signal. On the other hand, at the time of the reproduction, the reproduced line-sequential color difference signal was supplied to a circuit part made up from two switches and a 1 H delay circuit for simultaneously obtaining the two kinds of color difference signals, and then the color difference signals were supplied to a circuit part which produced the line-sequential color difference signal. Therefore, there was a problem in that the circuit construction became unnecessarily complex.
Further, when dubbing the color video signal according to the timeplex system, the color video signal passes through the recording system and the reproducing system of one recording and reproducing apparatus, and then passes through the recording system of another recording and reproducing system to be recorded on a magnetic tape, for example. In this case, the color video signal passes through a plurality of filter, frequency modulators, and frequency demodulators, and also passes through the time base compressing system and the time base expanding system. As a result, the frequency characteristic, the pulse characteristic, the linearity, and the like became deteriorated, and there was a problem in that a reproduced picture obtained from the dubbed color video signal had a deteriorated picture quality.